1. Field of the Invention
The invention relates to a short arc lamp. The invention relates especially to a short arc lamp with a reflection surface integrated in one piece, in which a reflection surface is formed in the lamp main part which forms the discharge space.
2. Description of Related Art
Short arc lamps are known which are produced as follows:
A lamp main part, which forms the discharge space in which there is a pair of electrodes, is made of a ceramic which is an opaque insulator material. PA1 In this lamp main part, a concave reflection surface is formed with a cross-sectional shape which is oval or parabolic. PA1 The opening of the reflection surface of the lamp main part which is used as the light exit part is covered with translucent material. PA1 a lamp main part which having an isolator component and in which a concave discharge space is formed with a reflection surface; PA1 a cathode and an anode located opposite one another in the discharge space in the focal position of the reflection surface spaced from one another; PA1 an annular, first feed component which is attached in the opening of the reflection surface of the lamp main part and to which a conductive electrode support component which supports the cathode is connected; PA1 a block-like, second feed component which is located in the base part on the side of the lamp main part opposite the opening and which supports the anode; and PA1 a plate-shaped, heat transferring component located between the base surface of the lamp main part and the second feed component, and having a thermal conductivity which is higher than that of the second feed component. PA1 a lamp main part which having an isolating component and in which a concave discharge space with a reflection surface is formed; PA1 a cathode and an anode are arranged spaced opposite each other in the discharge space in the focal position of the reflection surface; PA1 an annular first feed component which is attached in the open end of the reflection surface of the lamp main part and to which a conductive electrode support component which supports the cathode is connected; PA1 a block-like second feed component which is located in the base part on the side of the lamp main part which is opposite the opening, and which supports the anode; and PA1 the conductive electrode support component being straight, one end thereof being attached in the first feed component, and the other end thereof being loosely installed in a gap formed in the first feed component and secured such that it can move in the radial direction during thermal expansion, and the cathode being attached in the middle of this conductive electrode support component.
This short arc lamp with a reflection surface integrated in one piece has the advantage that the light source device is small, since the lamp need not be combined with a reflector. Furthermore, the lamp is extremely robust because it has an essentially cylindrical outside shape. Handling is therefore simple, and is used for those devices in which parallel beams from a strong point light source are desired, such as for a projection apparatus, a spectrometer or the like, in which a point light source is focused on a microscopically small surface and illumination and heating are produced via optical fibers or the like, as well as in similar contexts. A short arc lamp of this type is disclosed, for example, in Japanese patent SHO 54-37436 (U.S. Pat. No. 3,731,133).
FIG. 5 schematically shows a conventional short arc lamp with a reflection surface integrated in one piece. In the representation, in a concave discharge space D is formed in a lamp main part 1 consisting of an isolating component, there are a cathode 21 and an anode 22 opposite one another. On the inside of the discharge space D, a reflection surface 1a is formed. On the base surface 1b of the lamp main part 1 a block-like, second feed component 3 is installed in which the anode 22 is secured by brazing. The anode 22 extends from the middle opening 11 on the base side of lamp main part 1 into the discharge space 11. On the other hand, the cathode 21 is supported by a conductive, electrode supporting component 5 which is connected to an annular first feed component 4 which, in turn, is attached over the open end of the lamp main part 1. By turning on the first feed component 4 and the second feed component 3, a discharge takes place between the cathode 21 and the anode 22, by which the lamp is operated.
Since the cathode 21 and the anode 22 are located at the focal position of the reflection surface 1a, with a cross sectional shape which is oval or parabolic, the anode 22 is located in the vicinity of the central opening 11 on the base side of the lamp main part 1. When the lamp is being operated, especially the anode 22 reaches an extremely high temperature. In the lamp main part 1, therefore, the vicinity of the central opening 11 is greatly heated. Since the lamp main part 1 is formed from ceramic, it has low thermal conductivity. The heat in the vicinity of the central opening 11 is therefore poorly distributed within the lamp main part 1. This heat is, therefore, conducted and emitted to the second feed component 3 which is installed on the base surface 1b of the lamp main part 1.
When the anode 22, which reaches an extremely high temperature during operation, is brazed into the second feed component 3, a brazing filler metal of copper with a high melting point is needed. Therefore, the second feed component 3 is formed from an iron-based metal with a thermal stability temperature higher than the melting point of the copper brazing filler metal. However, an iron-based metal does not have very high thermal conductivity.
The heat conducted from the vicinity of the central opening 11 of the lamp main part 1 to the central area of the second feed component 3 is, therefore, poorly distributed in the radial direction. The heat is not distributed throughout the second feed component 3. This means that the heat radiation effect by the second feed component 3 is low.
Therefore, the heat is stored, especially in the vicinity of the central opening 11 of the lamp main part 1, so that the reflection surface in this area reaches a high temperature. During lamp operation over a long time, as a result, chemical conversion of the vacuum evaporated film of silver, aluminum or the like which is formed on the reflection surface takes place, by which the disadvantages of the formation of a diffusion surface, a color change and a reduction in the reflection factor have occurred. In the case of insufficient cooling in the lamp main part 1 which is formed from ceramic, a large amount of heat is locally stored, by which the defects occurred that a strong thermal distortion occurs and the lamp main part 1 breaks.
Another disadvantage is that the cathode 21 is supported by the conductive electrode support component 5 which is connected to the annular first feed component which is attached in the opening of the lamp main part. But conventionally, as is illustrated in FIG. 7, the cathode 21 is attached by brazing at the intersection of the three conductive electrode support parts 5 with individual ends attached in the first feed component 4 with equal distances of 120.degree. C. and extending into the center of the first feed component 4.
The electrodes reach an extremely high temperature during operation. Also, in the cathode, with a temperature lower than that of the anode, its rear end, i.e. the area connected to the conductive electrode support component 5, has a temperature of roughly 1000.degree. C., which is close to the melting point of the brazing filler metal. Since turning on and off are repeated periodically, as a result of the different coefficients of thermal expansion of the cathode 21 and the conductive electrode support component 5, a stress by thermal shock is exerted on the brazed point. However, since the cathode 21 is attached by the three conductive electrode support components 5, the thermal expansion of the respective conductive electrode support component 5 cannot be not absorbed. The cathode 21 is therefore subjected to complex stresses from three directions until finally cracks occur at the brazed point, the brazing filler metal melts, the position of the cathode changes and on the end the cathode 21 is occasionally separated from the conductive electrode support component 5.
Therefore, one end 5a of the conductive electrode support component 5 is connected to the first feed component 4, the other end 5b of the conductive electrode support component 5 is positioned in the center of the first feed component 4 and the cathode 21 is attached on this other end 5b of the conductive electrode support component 5 and used in practice (published Japanese application HEI 9-161727; U.S. Pat. No. 5,789,863) as is illustrated in FIGS. 5 and 6. FIG. 6 is a schematic of the installation arrangement of the first feed component 4 and the conductive electrode support component 5 to which the cathode 21 is attached, according to FIG. 5.
In periodically repeated turning on and off of the lamp, the tip of the conductive electrode support component 5, i.e. the location at which the cathode 21 is attached, is not subjected to complex stress by this arrangement either. Furthermore, mechanical strength can be reliably guaranteed when the cathode 21 is attached in the conductive electrode support component 5 by welding.
But, it was found that the cathode 21, which is attached to the tip as the free end of the conductive electrode support component 5, when the lamp is subjected to vibration, also vibrates easily and the arc fluctuates because the conductive electrode support component 5 is a cantilever. It was furthermore regarded as disadvantageous that the periodic damping is weak and the vibration lasts a relatively long time once it has started.
Since the conductive electrode support component 5, which reaches a high temperature during operation is attached with only one end to the first feed component 4, therefore, the thermal balance of the annular first feed component is adversely affected. The thermal balance of the lamp main component is therefore also adversely affected. The homogeneity of the gas in the discharge space is therefore adversely affected, and there are cases in which the light emitted from the lamp flickers.